The present invention relates to combined light emitter and focusing optics modules. Such modules, for example, can be used in scanners and the like for reading optically encoded information, such as bar codes.
A laser diode and focusing module will typically include a laser diode, at least one lens element for focusing light from the diode and means to fix the lens element at a desired distance from the laser diode so as to focus light from the diode at a point a predetermined distance in front of the module. Krichever et al., for example in their U.S. Pat. No. 4,923,281, teach telescoping two holding members of an emitting and focusing module against the force of a biasing spring positioned between the laser diode and the lens assembly to adjust the focusing of the light emitted by the module. One holding member is attached to the laser diode, and the other member holds the lens assembly for focusing the light from the laser diode. The second holder also provides an ellipsoidal aperture for the light passing through the lens. A series of notches and key elements prevents axial rotation between the cylindrical holders.
Laser diode and focusing modules may find use in a variety of light emitting devices. For example, such a module might be used in an optical pointer to allow a lecturer to produce a focused visible light beam spot on a screen or display to point out a particular feature for emphasis during the lecture. In such applications of the module, the larger the module, the larger and heavier the resulting device. Large size and weight of the device makes the device cumbersome and tiresome to use, particularly for protracted periods.
The presently preferred use of the laser diode and focusing module is as the emitting element of a device for reading optically encoded information, such as bar code symbols. To further emphasize problems relating to prior art module structures, the problems will be discussed in the context of bar code readers.
Bar code readers have become quite common because bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example to provide efficient inventories, tracking of work in progress, etc. To achieve these advantages, however, users or employees must be willing to consistently use the bar code readers. The readers therefore must be easy and convenient to operate and must produce little or no fatigue or discomfort during protracted use.
To decode a bar code symbol and extract a legitimate message, a bar code reader scans the symbol to produce an analog electrical signal representative of the scanned symbol. A variety of scanning devices are known. The scanner could be a wand type reader including an emitter and a detector fixedly mounted in the wand, in which case the user manually moves the wand across the symbol.
Alternatively, an optical scanner scans a light beam such as a laser beam across the symbol, and a detector senses the light reflected from the symbol. In either case, the detector senses reflected light from a spot scanned across the symbol, and the detector provides the analog scan signal representing the encoded information.
In a wand type reader and in most scanners the light source or emitter generates a light beam which is optically modified to form a beam spot of a certain size at the working distance and is directed toward a bar code symbol located in the vicinity of the working distance for reflection from the symbol. In readers using a laser as the emitter, the emitter and the optical focusing components can all be elements of a single laser and focusing module of the type described above.
Wand type readers are held and manipulated by hand. Many specific applications for the bar code scanners require that the optical scanner also is constructed in the form of a handheld of hand mounted unit, so that the user points the scanner at the object and operates a trigger to activate the scanning of the beam across the bar code. In such handheld readers, the emitter, optical focusing element and housing of the emitter and focusing module constitute a substantial percentage of the weight and volume. If the emitter and focusing module is large and heavy, the hand operated bar code reader will also be large and heavy. Consequently, the reader will be cumbersome to operate and will produce operator fatigue when used for long periods. Difficult operation, fatigue and discomfort in use all discourage an operator from actually using the reader of the bar code data input system. Reluctance to consistently use the reader can defeat the purposes and advantages of bar code data entry.
Commonly assigned application Ser. No. 07/193,265 filed May 11, 1988, now U.S. Pat. No. 5,144,120, discloses a mirrorless optical scanner, and application Ser. No. 07/699,417 filed on May 13, 1991 discloses incorporation of such a scanner in a modular scanner component system facilitating use of the scanner in a variety of different housing configurations. Several of the disclosed scanner configurations mount on the arm or hand of an operator. Commonly assigned application Ser. No. 07/787,458 filed on Nov. 4, 1991 discloses a scanner module for use in a ring mounted housing allowing the user to wear the scanner on a finger. The disclosure of each of these three copending applications is incorporated herein in its entirety by reference. To make the scanners worn on a hand, arm or finger practical, the light emitter and optics module used in such scanners must be extremely small. The conventional module package of a diameter=9.0 mm generally is too large for use in such scanners.
Furthermore, in many optical scanners, the laser beam is reflected back near the emitting and focusing module by the scanning mirror. To prevent the structure of the module from blocking or interfering with the path of the reflected beam dictates placement of the module at a point some distance below the path of the reflected beam. The larger the module, the larger the distance below the path of the reflected beam. The large distance below the path of the reflected beam results in a large incident angle between light from the laser emitter and the scanning mirror. A large incident angle, however, causes curvature distortion in the resultant scan line across the information surface. Such distortion complicates or prevents reading of truncated bar code symbols or two-dimensional symbols.
Typically, existing laser based bar code readers use a laser diode in a conventional module package of a diameter=9.0 mm. The larger diodes used in such modules, however, are more expensive than smaller laser diodes would be.
A need therefore exists to further reduce the size, weight and cost of the light emitter and focusing module for use in bar code readers and other devices which require an emitted beam of light.